Vapour phase epitaxy of wide Gap II–VI compounds

Abstract

ZnS and ZnSe epitaxial layers were grown by open-tube chemical vapour transport using a powder source and H 2 gas. Increased transport rates were brought about by halides (I 2, HCl) with, at the same time, relatively low source and growth temperatures ( T 1<850°C; T 2<600°C). Transport efficiencies have been calculated assuming equilibrium conditions. For growth temperatures in the range 650 to 750°C up to Δ T values of about 250°C and at low gas flows ( <20 1/h), qualitative agreement has been found between the experimental transport and growth rates with the theoretical ones. High quality layers were deposited under optimized conditions corresponding to this quasi-equilibrium case with sufficiently high substrate temperatures (>650°C) and at best at substrate orientations to about 4° off (100) towards (110). As the supersaturation is increased (higher Δ T, T growth<650°C) the growth rate is mainly determined by surface kinetics and by diffusion of material to and from a moving gas stream (boundary layer model). Using short growth times (<1 h), Zn excess, and relatively low diposition temperatures VPE methods have been successfully applied to grow low resistivity ZnSe on GaAs substrates with the same luminescent properties as high purity bulk samples. The epilayers exhibited even at room temperature dominant gap-near emission.